I've been producing 16 bit tiff files by exporting them from darktable. When I try to
open them in gimp 2.6.12, I get a Tiff Image Message telling me that
'directory is missing required "ImageLength" field'.
I also get an Import from TIFF window showing two pages, which I can
select. I can then Open these pages either as layers or images and Import
them. If I import the first page, I get something, but if I try to
import both or the second page I get the same Tiff Image Message.

I don't understand what is going on.

What could be special about the tiff file that is leading gimp to do
that? I can open the tiff file using eye of gnome, and I can open it
in photoprint. I can also open it in Inkscape. But I can't convert it
to a jpeg file using ImageMagick's convert. I get the same ImageLength
error. ImageMagick's display shows the image, but after it closes I get
the same sort of messages